Scientists from the University of Occupational and Environmental Health found that daily vitamin D supplements do not seem to prevent the development of type 2 diabetes in people already at high risk of the condition.
The research is published in The BMJ and was conducted by Tetsuya Kawahara et al.
Type 2 diabetes affects around 480 million people worldwide and is predicted to increase to 700 million by 2045.
Another half a billion people have impaired glucose tolerance or pre-diabetes (higher than normal blood sugar levels, that if left untreated, can develop into type 2 diabetes).
Weight loss and exercise can lower the risk of progression to type 2 diabetes, but are difficult to sustain, so new strategies are needed to tackle the problem.
Some studies have shown that vitamin D deficiency is associated with an increased risk of future diabetes, but trials of vitamin D supplements for preventing type 2 diabetes show inconsistent results.
In the study, the team examined whether eldecalcitol (an active form of vitamin D used to treat osteoporosis in Japan) could reduce the risk of developing type 2 diabetes among people with impaired glucose tolerance.
They tested 1,256 Japanese adults with impaired glucose tolerance recruited from three hospitals in Japan between June 2013 and August 2019.
Their average age was 61 (range 30-78) years, 46% were women, and 59% had a family history of type 2 diabetes.
Participants were assigned to receive either a standard daily dose of eldecalcitol (630 participants) or a placebo (626 participants).
During this period, the researchers found no meaningful differences between groups in those who developed diabetes or whose blood sugar levels returned to normal.
However, vitamin D might prevent type 2 diabetes in pre-diabetic patients with insufficient insulin secretion.
But this finding remains unclear and the researchers say further work is needed before any firm conclusions can be made.
They did, however, find a big increase in both lower back and hip bone mineral densities among those taking eldecalcitol compared with placebo.
No significant difference in serious adverse events was seen between the two groups.
If you care about supplements, please read studies about six vitamins that help stop complications in diabetes, and vitamin D may benefit men with advanced cancer.
For more information about supplements, please see recent studies about supplement that may help prevent vision loss, and results showing vitamin C may help treat cognitive impairment in older people.
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